Such devices are used in particular to influence an associated windscreen wiping system in dependence upon the quantity of precipitation on the windscreen of a motor vehicle.
A sensor device of the type specified in the preamble of the main claim has been disclosed in DE 38 23 300 C1. In that device, a heating apparatus comprising a self-regulating thermistor element is associated with a metallic reflecting means disposed in a beam guide element in order to bring the sensor device within a short time up to a specific temperature level of, for example, 40.degree. C. The apparatus achieves a reduction in the temperature-induced errors of the components of the sensor device and partial heating of the pane. However, DE 38 23 300 C1 does not disclose the special positioning and affixing methods described in the present disclosure.